This invention is concerned with a method of manufacturing a self-supporting filter unit, an apparatus suitable for use in carrying out such a method, said apparatus including a forming assembly, and also a self-supporting filter unit made using such a method.
Known dust filter units are in the form of bags which are supported against collapse by a framework of metal or other suitable material, air to be filtered being sucked through the bags from outside to the interior thereof so that dust particles and/or other debris are prevented by the material of the bags from passing to the interior and thus collected on the outer surface; the pore size of the fabric of these filter bags is selected according to the size of dust particles to be filtered from the gas flow.
Self-supporting filter units, i.e. units which do not require a framework of metal or other suitable material, are available; one such unit is supplied under the trademark "SINTAMATIC" by DCE Limited of Thurmaston, Leicester. This filter unit comprises a porous composite which is rigid and self-supporting, being made by a process in which a blend of granulated engineering polymers is dimensionally restrained and processed to produce a rigid porous composite element. The surface of this element is then treated with a P.T.F.E.-based solution to form a micro-porous skin. While this self-supporting filter has been shown to be generally satisfactory in performance, it is somewhat expensive to provide and the production process is relatively complex.